The increasing use of computers in modern society has led to a corresponding increase in the use of peripheral devices to augment the outside memory available to the computer. A computer basically has two types of memories--ROM (Read Only Memory) and RAM (Random Access Memory). ROM is exemplified by the non-volatile memory that is built into the interpreter portion of the computer to translate the particular language used by the operator into machine language used by the processor.
RAM is exemplified by the volatile memory which stores the program and information that the operator loads into the computer. The amount of information which can be loaded into the computer is limited by the memory capacity of the computer and, to the extent the memory capacity is of a volatile type, may be subject to loss if there is a power failure or if the computer is turned off, either purposely or inadvertently.
Memory can be expanded by the use of peripherals. For example, a tape recorder can be interfaced with the computer and used to effect long-term storage of information. Thus, whatever program, information or other data that can be entered into memory can be preserved for repetitive use by virtue of substantially permanent storage on a relatively inexpensive tape cassette.
Another type of memory storage outside the computer comprises a circular disk of thin plastic coated with magnetic material of the same general type used on cassette tapes. This magnetic disk looks like a flexible, 45 rpm record and is called a "floppy disk."
The disk itself is encased in a protective envelope, generally cardboard, and the combined disk and envelope are insertably received within a disk drive unit. The center of the protective envelope is provided with an access aperture that is concentrically disposed with respect to a drive aperture located in the center of the floppy disk. Jaws within the drive unit engage the drive aperture, through the access aperture in the protective envelope, to rotate the disk within the envelope at speeds of several hundred rpm. Information stored on the disk is transferred to the memory within the computer by virtue of a reading/recording head that is provided in the disk drive unit and positioned in juxtaposition to the disk through an access window in the envelope. Similarly, information within the computer can be transferred to, and stored on, a floppy disk.
Although the floppy disk system is generally more expensive than the cassette system, the transfer of information back and forth between the computer and the floppy disk system occurs at a small fraction of the time required for the cassette system. For example, a program that would require three and a half minutes to load from a cassette could be loaded in less than twenty seconds from a floppy disk system.
All considered, the floppy disk system is a powerful peripheral for a computer. However, there appears to be one major problem encountered by users of the floppy disk system--i.e., random damage to the drive aperture of the disk itself after it has been insertably received within the disk drive unit. Because the disk must be free to rotate within its protective envelope, the inside dimension of the generally square envelope is preferably somewhat greater than the outside diameter of the disk--thus providing some necessary "slop" between the disk and the protective envelope within which the disk is encased.
The slop necessary to assure free rotation of the disk within its protective envelope also permits the disk to move laterally within its envelope when the disk is not received within the drive unit. As such, when the disk assembly is inserted into the drive unit, there is no assurance that the drive aperture in the center of the disk will be accurately registered with the jaws of the drive unit that grasp and rotate the disk within its envelope.
Successive engagement of the disk with the drive jaws when the disk is out of register deteriorates the drive aperture of the disk itself.